Gas turbine engine braking method

ABSTRACT

The present disclosure discloses an engine braking system, especially for vehicles powered by a gas turbine. The engine braking system allows for control of engine braking force; control of over-speed of the power turbine and further includes means of recovering some or all of the braking energy of the engine braking system. Dissipative engine braking devices include an auxiliary compressor, or electrical generator, or an eddy current clutch or an eddy current brake, or fluid pump. Several methods of controlling the engine braking force of a dissipative braking device are disclosed and include (1) a continuously variable transmission (“CVT”); (2) an electrical generator and an optional thermal storage device; (3) an eddy current clutch; and (4) a fluid pump system. The various control devices may be operated automatically by appropriate algorithms. One of these control methods utilizes an eddy current clutch assembly. An innovative configuration of eddy current clutch assembly based on a brushless alternator is disclosed. Additional innovations include vehicle braking systems that utilize some or all the braking features to recoup a portion of braking energy available with either or both of a hybrid transmission and a dissipative braking device such as a compressor, an electrical generator or a fluid pump system.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the benefits, under 35 U.S.C. §119(e), of U.S. Provisional Application Ser. No. 61/440,746 entitled “Gas Turbine Engine Braking Method” filed on Feb. 8, 2011, which is incorporated herein by reference.

FIELD

The present disclosure on relates generally to gas turbine engine systems and specifically to a method and apparatus that can provide control of power turbine over-speed and engine braking to a vehicle.

BACKGROUND

There is a growing requirement for alternate fuels for vehicle propulsion. These include fuels such as natural gas, bio-diesel, ethanol, butanol, hydrogen and the like. Means of utilizing fuels needs to be accomplished more efficiently and with substantially lower carbon dioxide emissions and other air pollutants such as NOxs.

The gas turbine or Brayton cycle power plant has demonstrated many attractive features which make it a candidate for advanced vehicular propulsion. Gas turbine engines have the advantage of being highly fuel flexible and fuel tolerant. Additionally, these engines burn fuel at a lower temperature than reciprocating engines so produce substantially less NOxs per mass of fuel burned.

However, the gas turbine does not allow the normal “engine braking” or “compression braking” feature that is extensively used in piston-type engines. The utility of these engines, especially for use in large vehicles such as Class 8 trucks, can be substantially improved by providing an engine braking capability analogous to the Jacobs brake used by piston engine powered trucks.

In addition, configurations of gas turbine engines which employ a free power turbine require additional means to control over-speeding of the free power turbine. Such over-speeding can occur in vehicle or other applications, for example, when the load is abruptly reduced or disconnected.

U.S. Pat. No. 3,817,343 “Installation for Brake of Motor Vehicles Which Are Driven from a Gas Turbine” discloses a means for the braking of motor vehicles which are driven by a gas turbine engine comprising a free output or free power turbine, by means of a rotary compressor that is arranged in or parallel to the transmission and is in the power path from the free working turbine to the driven wheels. U.S. Pat. No. 3,817,343 does not teach how to control the braking force of the braking compressor nor how to utilize the output of the braking compressor for recovering useful energy.

There thus remains a need for compact, controllable engine braking apparatus to improve engine braking performance so as to assist the vehicle's foundation braking system. There is also a need, for vehicles powered by gas turbine engines, for a means of over-speed control of the free power turbine.

SUMMARY

Accordingly, it is an object of the present disclosure to provide an engine braking system, especially for vehicles powered by a gas turbine. The engine braking system of the present disclosure allows for control of auxiliary engine braking force; control of over-speed of the power turbine; generation of air used for quenching hot recuperator gases to assist in engine turndown; and further includes means of recovering some or all of the braking energy of the engine braking system.

As mentioned, U.S. Pat. No. 3,817,343 teaches use of a rotary compressor which can act as an auxiliary braking systems on large vehicles such as Class 8 trucks. U.S. Pat. No. 3,817,343 does not teach how to control the braking force nor does it teach how to utilize the energy dissipated by the braking compressor.

Several braking devices are disclosed. These include energy dissipative devices such as, for example, a compressor, an electrical generator, a fluid pump system and an eddy current brake or clutch. The present disclosure includes several methods of controlling the engine braking force of a braking device. Such control devices disclosed herein include (1) a continuously variable transmission (“CVT”); (2) an electrical generator and an optional thermal storage device; (3) an eddy current clutch; and (4) a fluid pump system. As can be appreciated, the various control devices may be controlled automatically by an appropriate control algorithm which is responsive to the data from various shaft rpms, free power turbine rpms and braking instructions.

One of these control methods utilizes an eddy current clutch. An innovative configuration of eddy current clutch based on a brushless alternator is disclosed.

Additional innovations disclosed herein include vehicle braking systems that utilize some or all the braking features to recoup a portion of braking energy available with either or both of a hybrid transmission and a braking compressor.

It is noted that the engine braking system of the present disclosure is a form of dynamic braking since the braking force applied to the vehicle only exists when the vehicle is in motion and when the engine braking system is caused to be connected to the vehicle's drive train.

These and other advantages will be apparent from the disclosure contained herein.

In one embodiment, a vehicle is disclosed comprising a gas turbine engine and a transmission, the gas turbine engine comprising at least one turbo-compressor spool assembly, wherein the at least one turbo-compressor spool assembly comprises a compressor in mechanical communication with a turbine, the turbine outputting a gas, and a free power turbine in fluid communication with the turbine, the free power turbine being driven by the outputted gas, a system comprising a braking device in mechanical communication with the free power turbine and the transmission to at least one of dissipate energy of the free power turbine and provide a braking force to the vehicle, wherein at least one of the following is true: (a) the braking device comprises a compressor selectively mechanically engaged and disengaged from the free power turbine and/or the transmission of the vehicle by a clutch assembly: (b) the braking device comprises a continuously variable transmission; (c) the braking device comprises an electrical generator configured to generate a selected amount of electrical energy; (d) the braking device comprises at least one of an eddy current clutch and an eddy current brake; and (e) the braking device comprises a fluid pump circuit.

In another embodiment, a method is disclosed system for a vehicle comprising a gas turbine engine and a transmission comprising at least one turbo-compressor spool assembly, the at least one turbo-compressor spool assembly comprising a compressor in mechanical communication with a turbine, the turbine outputting a gas, a free power turbine in fluid communication with the turbine, the free power turbine being driven by the outputted gas, and a braking device in mechanical communication with the free power turbine and the transmission, the method comprising performing at least one of the following steps: (a) in response to a sensed revolutions-per-minute of the free power turbine, selectively engaging and disengaging a braking device from mechanical communication with the free power turbine, the braking device retarding rotation of the free power turbine; (b) in response to a sensed braking request of the vehicle, selectively engaging and disengaging a braking device from mechanical communication with the free power turbine, the braking device providing a braking force to the vehicle; (c) varying, by an continuously variable transmission, a gear ratio continuously between first and second gear ratios, the gear ratio being for a mechanical linkage between a braking device and the clutch assembly; (d) generating, by an electrical generator, a selected amount of electrical energy to provide at least one of a selected amount of retardation force against rotation of the free power turbine and a selected amount braking force to the vehicle; (e) applying torque by at least one of an eddy current brake and eddy current clutch to provide at least one of a selected amount of retardation force against rotation of the free power turbine and a selected amount braking force to the vehicle; and (f) intermittently operating a fluid pump in mechanical communication with the free power turbine to provide at least one of a selected amount of retardation force against rotation of the free power turbine and a selected amount braking force to the vehicle.

In yet another embodiment, a vehicle is disclosed, comprising an engine, a transmission, a braking device to maintain or reduce the ground velocity of the vehicle; and at least one of the following braking device control devices: 1) a continuously variable transmission positioned mechanically with respect to the braking device, the transmission and the engine, 2) an electrical generator configured to generate a selected amount of electrical energy to provide a selected amount of retardation force against rotation of a shaft of the engine, 3) at least one of an eddy current clutch and eddy current brake positioned mechanically with respect to the braking device, the transmission and the engine, and a pump and restrictor valve in fluid communication with the braking device.

In another embodiment, a tangible or non-transient computer readable medium is disclosed comprising microprocessor-executable instructions operable to perform at least the following steps: a) sensing at least one of a revolutions per minute (“rpms”) of a free power turbine, at least one of an on and off state of a braking device clutch, at least one of an on and off state of a transmission clutch, and a braking device control setting; b) based on the sensed at least one of a revolutions per minute (“rpms”) of a free power turbine, at least one of an on and off state of a braking device clutch, at least one of an on and off state of a transmission clutch, and a braking device control setting, determining that the free power turbine requires over-speed control; c) in response to step (b), disengaging the transmission clutch and engaging the braking device clutch; d) reducing the rpms of the free power turbine by controlling an amount of energy dissipation of the braking device; e) during step (d), sensing rpms of the free power turbine and reducing the rpms of the free power turbine until the rpms of the free power turbine are reduced to less than or equal to a selected value; and f) when the rpms of the free power turbine are less than the selected value, disengaging the braking device clutch.

In another embodiment, a tangible or non-transient computer readable medium is disclosed comprising microprocessor-executable instructions operable to perform at least the following steps: a) sensing at least one of an on and off state of braking device clutch, at least one of an on and off state of a transmission clutch, a vehicle ground velocity, a transmission gear setting, and a braking device control setting; b) based on the sensed at least one of a vehicle ground velocity, at least one of an on and off state of a braking device clutch, at least one of an on and off state of a transmission clutch, and a braking device control setting, determining that engine braking is required; c) in response to step (b), engaging the braking device clutch and engaging the transmission clutch for engine braking; d) increasing a vehicle braking force opposing a direction of motion of the vehicle by controlling an amount of energy dissipation of the braking device; e) during step (d), sensing a vehicle ground velocity and applying the engine braking force until the vehicle ground velocity is less than or equal to a selected value; and f) when the vehicle ground velocity is less than or equal to the selected value, disengaging the braking device clutch.

The above-described embodiments and configurations are neither complete nor exhaustive. As will be appreciated, other embodiments of the invention are possible utilizing, alone or in combination, one or more of the features set forth above or described in detail below.

The following definitions are used herein:

The term “a” or “an” entity refers to one or more of that entity. As such, the terms “a” (or “an”), “one or more” and “at least one” can be used interchangeably herein. It is also to be noted that the terms “comprising”, “including”, and “having” can be used interchangeably.

The term automatic and variations thereof, as used herein, refers to any process or operation done without material human input when the process or operation is performed. However, a process or operation can be automatic, even though performance of the process or operation uses material or immaterial human input, if the input is received before performance of the process or operation. Human input is deemed to be material if such input influences how the process or operation will be performed. Human input that consents to the performance of the process or operation is not deemed to be “material”.

A bell housing is a term for the portion of the transmission that covers the flywheel and the clutch or torque converter of the transmission on vehicles powered by internal combustion engines. This housing is bolted to the engine block and derives its name from the bell-like shape that its internal components necessitate. The starter motor is usually mounted here, and engages with a ring gear on the flywheel. On the opposite end to the engine is usually bolted to the gearbox. The above is the normal arrangement for an in-line transmission system for a conventional rear wheel drive or all wheel drive vehicle. The arrangement for a transverse mounted engine and transmission for a front wheel drive vehicle has the gear box and differential below the engine and consequently the bell housing is a simple cover for the flywheel.

A bull gear is the larger of two gears that are in engagement. The smaller gear is usually referred to as a pinion gear.

A brushless alternator is composed of two alternators built end-to-end on one shaft. Smaller brushless alternators may look like one unit but the two parts are readily identifiable on the large versions. The larger of the two sections is the main alternator and the smaller one is the exciter. The exciter has stationary field coils and a rotating armature (power coils). The main alternator uses the opposite configuration with a rotating field and stationary armature. A bridge rectifier, called the rotating rectifier assembly, is mounted on a plate attached to the rotor. Neither brushes nor slip rings are used, which reduces the number of wearing parts. The main alternator has a rotating field as described above and a stationary armature (power generation windings). Varying the amount of current through the stationary exciter field coils varies the 3-phase output from the exciter. This output is rectified by a rotating rectifier assembly, mounted on the rotor, and the resultant DC supplies the rotating field of the main alternator and hence alternator output. The result of all this is that a small DC exciter current indirectly controls the output of the main alternator.

As used herein, a clutch is a device used to connect or disconnect flow of power from one part of a transmission from another. For example, in a typical reciprocating engine vehicle, the clutch is the mechanism in the drive train that connects the engine crankshaft to or disconnects it from the gearbox thus with the remainder of the drive train.

The term computer-readable medium as used herein refers to any tangible or non-transient storage and/or transmission medium that participate in providing instructions to a processor for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media includes, for example, NVRAM, or magnetic or optical disks. Volatile media includes dynamic memory, such as main memory. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, or any other magnetic medium, magneto-optical medium, a CD-ROM, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, a solid state medium like a memory card, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read. A digital file attachment to e-mail or other self-contained information archive or set of archives is considered a distribution medium equivalent to a tangible or non-transient storage medium. When the computer-readable media is configured as a database, it is to be understood that the database may be any type of database, such as relational, hierarchical, object-oriented, and/or the like. Accordingly, the disclosure is considered to include a tangible or non-transient storage medium or distribution medium and prior art-recognized equivalents and successor media, in which the software implementations of the present disclosure are stored.

A Continuously Variable Transmission or CVT has a low gear ratio and a high gear ratio with infinitely many ratios in-between. The advantage of a CVT is the ability to keep the engine's RPMs in their optimum power output range for all operating conditions. A vehicle with a CVT transmission can be readily diagnosed with software. Unlike traditional automatic transmissions, continuously variable transmissions don't have a gearbox with a set number of gears, which means they don't have interlocking toothed wheels. The most common type of CVT operates on a pulley system that allows an infinite variability between highest and lowest gears with no discrete steps or shifts. Other types of CVTs include toroidal and hydrostatic.

DC bus means DC link and the terms may be used interchangeably.

The terms determine, calculate and compute and variations thereof, as used herein, are used interchangeably and include any type of methodology, process, mathematical operation or technique.

A differential connects a drive shaft to axles. While the differential may provide gear reduction, its primary purpose is to change the direction of rotation.

A drive train is the part of a vehicle or power generating machine that transmits power from the engine to the driven members, such as the wheels on a vehicle, by means of any combination of belts, fluids, gears, flywheels, electric motors, clutches, torque converters, shafts, differentials, axles and the like.

An eddy current brake is a type of electromagnetic brake in which torque is applied to a rotating shaft by means of eddy currents induced by a magnetic field set up by a conductor carrying direct current in a fixed member forming one side of the brake and inducing an opposing current in a conductor in a rotating member forming the other side of the brake.

An eddy current clutch is a type of electromagnetic clutch in which torque is transmitted by means of eddy currents induced by a magnetic field set up by a conductor carrying direct current in a member forming one side of the clutch and inducing an opposing current in a conductor in a rotating member forming the other side of the clutch.

An energy storage system refers to any apparatus that acquires, stores and distributes mechanical or electrical energy which is produced from another energy source such as a prime energy source, a regenerative braking system, a third rail and a catenary and any external source of electrical energy. Examples are a battery pack, a bank of capacitors, a pumped storage facility, a compressed air storage system, an array of a heat storage blocks, a bank of flywheels or a combination of storage systems.

An engine is a prime mover and refers to any device that uses energy to develop mechanical power, such as motion in some other machine. Examples are diesel engines, gas turbine engines, microturbines, Stirling engines and spark ignition engines.

An engine braking device as used herein is an auxiliary braking apparatus that dissipates engine power when engaged. When engaged, the engine braking device may dissipate power from the engine when the transmission clutch is not engaged and may increase vehicle braking force when the transmission clutch is engaged.

A free power turbine as used herein is a turbine which is driven by a gas flow and whose rotary power is the principal mechanical output power shaft. A free power turbine is not connected to a compressor in the gasifier section, although the free power turbine may be in the gasifier section of the gas turbine engine. A power turbine may also be connected to a compressor in the gasifier section in addition to providing rotary power to an output power shaft.

The foundation braking system of a vehicle, as used herein, comprise the drum and/or disc brakes associated with all or most of the wheels of a vehicle.

A gear box as used herein is a housing that includes at least one gear set. Typically, a gear box on a vehicle includes switchable gear sets to provide multiple gear ratios, with the ability to switch between them as speed varies. Directional (forward and reverse) control may also be provided. This switching may be done manually or automatically.

A gear set as used herein is a single ratio gear assembly.

Jake brake or Jacobs brake describes a particular brand of engine braking system. It is used generically to refer to engine brakes or compression release engine brakes in general, especially on large vehicles or heavy equipment. An engine brake is a braking system used primarily on semi-trucks or other large vehicles that modifies engine valve operation to use engine compression to slow the vehicle. They are also known as compression release engine brakes.

A mechanical-to-electrical energy conversion device refers an apparatus that converts mechanical energy to electrical energy or electrical energy to mechanical energy. Examples include but are not limited to a synchronous alternator such as a wound rotor alternator or a permanent magnet machine, an asynchronous alternator such as an induction alternator, a DC generator, and a switched reluctance generator. A traction motor is a mechanical-to-electrical energy conversion device used primarily for propulsion.

The term module as used herein refers to any known or later developed hardware, software, firmware, artificial intelligence, fuzzy logic, or combination of hardware and software that is capable of performing the functionality associated with that element. Also, while the disclosure is presented in terms of exemplary embodiments, it should be appreciated that individual aspects of the disclosure can be separately claimed

A permanent magnet motor is a synchronous rotating electric machine where the stator is a multi-phase stator like that of an induction motor and the rotor has surface-mounted permanent magnets. In this respect, the permanent magnet synchronous motor is equivalent to an induction motor where the air gap magnetic field is produced by a permanent magnet. The use of a permanent magnet to generate a substantial air gap magnetic flux makes it possible to design highly efficient motors. For a common 3-phase permanent magnet synchronous motor, a standard 3-phase power stage is used. The power stage utilizes six power transistors with independent switching. The power transistors are switched in ways to allow the motor to generate power, to be free-wheeling or to act as a generator by controlling frequency.

Over-speed control of a free power turbine means control of the rpms of a free power turbine by preventing the rpms from increasing beyond a selected value. Typically, a free power turbine will over-speed if the gas driving the turbine remains on while the load (transmission or electrical generator for example) is rapidly or abruptly turned off.

A pinion is the smaller of two gears that are in engagement. The larger gear is usually referred to as a bull gear.

A planetary gear (also known as an epicyclic gear) is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear (also known as a sun pinion). Typically, the planet gears are mounted on a planet carrier plate which itself may rotate relative to the sun gear. Planetary gearing systems also incorporate the use of an outer ring gear or orbit gear which meshes with the planet gears. In this gear system, the sun gear engages all three planet gears simultaneously. All three are attached to a planet carrier plate, and they engage the inside of the ring gear. Because there are three planet gears instead of one, the arrangement is extremely rugged. The output shaft may be attached to the ring gear, and the planet carrier may be held stationary. Alternately the output shaft may be attached to the planet carrier and the ring gear may be held stationary. Planetary gear sets can produce different gear ratios depending on which gear is used as the input, which gear is used as the output and which gear is held stationary. For instance, if the input is the sun gear the ring gear is held stationary and the output shaft is attached to the planet carrier, a particular gear ratio is obtained. In this case, the planet carrier and planets orbit the sun gear, so instead of the sun gear having to rotate six times for the planet carrier to rotate once, it has to spin seven times. This is because the planet carrier circles the sun gear once in the same direction as it was spinning, subtracting one revolution from the sun gear. So in this case, a 7:1 reduction is obtained. If the sun gear is held stationary and the output is from the planet carrier and the input is to the ring gear, a 1.17:1 gear reduction would be obtained.

A prime power source refers to any device that uses energy to develop mechanical or electrical power, such as motion in some other machine. Examples are diesel engines, gas turbine engines, microturbines, Stirling engines, spark ignition engines and fuel cells.

A power control apparatus refers to an electrical apparatus that regulates, modulates or modifies AC or DC electrical power. Examples are an inverter, a chopper circuit, a boost circuit, a buck circuit or a buck/boost circuit.

Power density as used herein is power per unit volume (watts per cubic meter).

A recuperator is a heat exchanger that transfers heat through a network of tubes, a network of ducts or walls of a matrix wherein the flow on the hot side of the heat exchanger is typically exhaust gas and the flow on cold side of the heat exchanger is typically gas (for example, air or a fuel-air mixture) entering the combustion chamber.

Regenerative braking is the same as dynamic braking except the electrical energy generated is recaptured and stored in an energy storage system for future use.

Specific power as used herein is power per unit mass (watts per kilogram).

Spool means a group of turbo machinery components on a common shaft.

A thermal energy storage module is a device that includes either a metallic heat storage element or a ceramic heat storage element with embedded electrically conductive wires. A thermal energy storage module is similar to a heat storage block but is typically smaller in size and energy storage capacity.

As used herein, a transmission is the part of a vehicle or power generating machine that transmits power from the output shaft of an engine to a drive shaft by means of any combination of belts, fluids, gears, flywheels, electric generators, clutches, torque converters and the like. A transmission may be a manual transmission or an automatic transmission. A transmission may be an all-mechanical apparatus or an apparatus with both mechanical and electrical components. The latter may also be called a hybrid transmission. In British usage, the term transmission typically refers to the whole drive train, including gearbox, clutch, drive shaft, differential and axles. In American usage for reciprocating engines, the transmission is often taken to be the gearbox between the clutch assembly in the bell housing and the drive shaft. The more general definition is used herein (power transmission apparatuses from the output shaft of an engine to a drive shaft) unless specifically defined otherwise.

A traction motor is a motor used primarily for propulsion such as commonly used in a locomotive. Examples are an AC or DC induction motor, a permanent magnet motor and a switched reluctance motor.

A turbine is any machine in which mechanical work is extracted from a moving fluid by expanding the fluid from a higher pressure to a lower pressure.

Turbine Inlet Temperature (TIT) as used herein refers to the gas temperature at the outlet of the combustor which is closely connected to the inlet of the high pressure turbine and these are generally taken to be the same temperature.

A turbo-compressor spool assembly as used herein refers to an assembly typically comprised of an outer case, a radial compressor, a radial turbine wherein the radial compressor and radial turbine are attached to a common shaft. The assembly also includes inlet ducting for the compressor, a compressor rotor, a diffuser for the compressor outlet, a volute for incoming flow to the turbine, a turbine rotor and an outlet diffuser for the turbine. The shaft connecting the compressor and turbine includes a bearing system.

Any reference to a braking compressor is assumed to include other dissipating apparatuses such as electric motors or other mechanical, fluid, magnetic, electrical and/or electromagnetic devices that consume energy.

The phrases “at least one”, “one or more”, and “and/or” are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions “at least one of A, B and C”, “at least one of A, B, or C”, “one or more of A, B, and C”, “one or more of A, B, or C” and “A, B, and/or C” means A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B and C together.

The preceding is a simplified summary of the disclosure to provide an understanding of some aspects of the disclosure. This summary is neither an extensive nor exhaustive overview of the disclosure and its various aspects, embodiments, and/or configurations. It is intended neither to identify key or critical elements of the disclosure nor to delineate the scope of the disclosure but to present selected concepts of the disclosure in a simplified form as an introduction to the more detailed description presented below. As will be appreciated, other aspects, embodiments, and/or configurations of the disclosure are possible utilizing, alone or in combination, one or more of the features set forth above or described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the disclosure. In the drawings, like reference numerals refer to like or analogous components throughout the several views

FIG. 1 is a schematic of a prior art gas turbine engine architecture.

FIG. 2 is a schematic of a gas turbine engine architecture with a prior art braking compressor connected to a transmission.

FIG. 3 is a schematic of a gas turbine engine architecture with a prior art braking compressor connected to a free power turbine.

FIG. 4 is a schematic of prior art control for a braking compressor.

FIGS. 5 a and 5 b illustrate an example, in end view, of how a braking compressor can be geared.

FIG. 6 illustrates an example, in plan view, of how a braking compressor can be geared.

FIG. 7 illustrates an example, in plan view, of how a braking compressor can be controlled using a Continuously Variable Transmission (“CVT”).

FIG. 8 illustrates in detail a braking compressor combined with a high speed generator and thermal energy storage module.

FIG. 9 illustrates, in plan view, an example of how a braking compressor can be used with a high speed generator and thermal energy storage module.

FIG. 10 illustrates a brushless eddy current clutch with DC excitation.

FIG. 11 illustrates a brushless eddy current clutch with AC excitation.

FIG. 12 illustrates an example, in plan view, of how a braking compressor can be controlled using an eddy current clutch.

FIG. 13 illustrates a fluid pump circuit for dissipating energy.

FIG. 14 is an isometric view of prior art planetary gears.

FIGS. 15 a and 15 b illustrate how a planetary gear system can be used for control of a braking compressor.

FIG. 16 illustrates an example, in plan view, of how a braking compressor can be controlled using a fluid pump and planetary gear system.

FIG. 17 is a schematic of a hybrid braking system for a gas turbine engine.

FIG. 18 is a schematic of a first alternate hybrid braking system for a gas turbine engine.

FIG. 19 is a schematic of a second alternate hybrid braking system for a gas turbine engine.

FIGS. 20 a and 20 b are flow charts for free power turbine over-speed control.

FIGS. 21 a and 21 b are flow charts for engine braking control.

DETAILED DESCRIPTION Prior Art Preferred Engine

A preferred engine type is a high efficiency gas turbine engine because it typically has lower NOx emissions, is more fuel flexible, fuel tolerant and has lower maintenance costs. For example, an intercooled recuperated gas turbine engine in the 10 kW to 750 kW range is available with thermal efficiencies above 40%. A schematic of an intercooled recuperated gas turbine engine is shown in FIG. 1.

FIG. 1 is schematic of the component architecture of a prior art multi-spool gas turbine engine. Air (or in some configurations, an air-gaseous fuel mix) is ingested into a low pressure compressor 1. The outlet of the low pressure compressor 1 passes through an intercooler 2 which removes a portion of heat from the gas stream at approximately constant pressure. The gas then enters a high pressure compressor 3. The outlet of high pressure compressor 3 passes through a recuperator 4 where a significant portion of the heat from the exhaust gas is transferred, at approximately constant pressure, to the gas flow from high pressure compressor 3. The further heated gas from recuperator 4 is then directed to a combustor 5 where a fuel is reacted or burned, adding a small mass of fuel and substantial energy to the gas flow at approximately constant pressure. The gas emerging from combustor 5 then enters a high pressure turbine 6 where work is done by high pressure turbine 6 to operate high pressure compressor 3. The gas from high pressure turbine 6 then enters a low pressure turbine 7 where work is done by low pressure turbine 7 to operate low pressure compressor 1. The gas from low pressure turbine 7 then enters a free power turbine 8. The shaft of free power turbine 8, in turn, drives a transmission 11 which may be an electrical, mechanical or hybrid transmission for a vehicle. Alternately, the shaft of the free power turbine can drive an electrical generator or alternator. This engine design is described, for example, in U.S. patent application Ser. No. 12/115,134 filed May 5, 2008, entitled “Multi-Spool Intercooled Recuperated Gas Turbine”, which is incorporated herein by this reference.

Variations of this engine architecture may include a reheater and/or thermal energy storage devices such as described, for example, in U.S. patent application Ser. No. 13/175,564, entitled “Improved Multi-Spool Intercooled Recuperated Gas Turbine” and U.S. patent application Ser. No. 12/777,916, entitled “Gas Turbine Energy Storage and Conversion System”, both of which are incorporated herein by reference.

Prior Art Engine Braking Using a Compressor

U.S. Pat. No. 3,817,343 entitled “Installation for Brake of Motor Vehicles Which Are

Driven from a Gas Turbine” teaches a rotary compressor which acts as a dissipating apparatus that can convert shaft power into an air discharge by converting mechanical energy into kinetic and heat energy of a gas, namely air. This apparatus can have utility for braking systems on vehicles, especially large vehicles such as Class 8 trucks. The dissipating compressor disclosed in U.S. Pat. No. 3,817,343 does not teach how to control the braking force nor does it teach how to utilize the energy dissipated by the braking compressor.

Braking Compressor Locations

FIG. 2 is a schematic of a prior art gas turbine engine architecture with braking compressor connected to a transmission. The engine of FIG. 2 is identical to the engine shown in FIG. 1. A braking compressor 12 is shown connected to a transmission 9 by clutch apparatus 11. Transmission 9 connects the output shaft of free power turbine 8 to the vehicle's drive shaft. The transmission may be an electrical, mechanical or hybrid transmission. Transmission 9 may be, for example, a mechanical transmission appropriate to a reciprocating engine. If so, it can be adapted to a gas turbine engine which may include a braking compressor capability. This can be accomplished by adding a reducing gear assembly to reduce rpms from the turbine output to the rpms of a conventional transmission and a second clutch as described in FIG. 6. As can be appreciated, this configuration can be used on any transmission with any engine. As will be discussed subsequently, clutch 11 is optional. As can be appreciated, other dissipating devices can be used in place of a braking compressor. These include, for example, an electrical generator or a fluid pump system.

FIG. 3 is a schematic of a prior art gas turbine engine architecture with braking compressor connected to a free power turbine. The engine of FIG. 3 is identical to that of FIG. 1. A braking compressor 12 is shown connected to a free power turbine 8 by clutch apparatus 11. This configuration can be applied to a vehicle with any type of transmission. This means of driving braking compressor 12 is dependent on the packaging of the gas turbine engine components. For example, if the low pressure turbine outlet is connected directly to the free power turbine inlet, it may be preferable to use the arrangement shown in FIG. 2. As will be discussed subsequently, clutch 11 is optional.

Control of Braking Compressor Air Flow

FIG. 4 is a schematic of prior art control for a braking compressor. In FIG. 4 a, a braking compressor 12 is shown connected to a transmission 9 by a clutch assembly 11. There is an inlet air flow control device 13 to control the flow of inlet air 15 and an outlet air flow control device 14 to control the flow of outlet air 16. The braking compressor 12 may have either an inlet air flow control device 13 or an outlet air flow control device 14 or both. The inlet air flow device may be a valve, a variable position nozzle or the like. If there is only an inlet air flow control device, then there would have to be a throat on the outlet of the braking compressor to allow pressure buildup so that the compressor could extract energy. The outlet air flow device may be a valve, a variable position nozzle, an iris opening plate, a venturi throat or the like. If there is only an outlet air flow control device, then there may or may not be an inlet air flow control device. The control of the braking compressor is such that surge and stall of the compressor are avoided.

In FIG. 4 b, a braking compressor 12 is shown connected to a free power turbine 8 by a clutch assembly 11. There is an inlet air flow control device 13 to control the flow of inlet air 15 and an outlet air flow control device 14 to control the flow of outlet air 16. The braking compressor 12 may have either an inlet air flow control device 13 or an outlet air flow control device 14 or both. The inlet air flow device may be a valve, a variable position nozzle or the like. If there is only an inlet air flow control device, then there would have to be a throat on the outlet of the braking compressor to allow pressure buildup so that the compressor could extract energy. The outlet air flow device may be a valve, a variable position nozzle, an iris opening plate, a venturi throat or the like. If there is only an outlet air flow control device, then there may or may not be an inlet air flow control device. The control of the braking compressor is such that surge and stall of the compressor are avoided.

Present Disclosure

In this disclosure, a braking compressor is often used to illustrate a braking device that can dissipate energy either from an over-speeding free turbine or to provide the effect of engine braking. As can be appreciated, other dissipating apparatuses can be used to dissipate energy either from an over-speeding free turbine or to provide the effect of engine braking. These include electric generators, pump systems, eddy current brakes and clutches or other mechanical, fluid, magnetic, electrical and/or electromagnetic devices that consume energy.

The method and apparatus of the present disclosure can be adapted to either a vehicle powered by a gas turbine engine, by a reciprocating piston engine or indeed any engine. If applied to an engine running in the rpm range of 10,000 rpm or less, increasing gears will normally be required to engage a braking compressor in order for the braking power to be developed by an auxiliary compressor which, for a reasonable size, will be more compact and efficient at higher rpms, typically in the range of about 40,000 rpm to about 150,000 rpm.

An innovation of the present disclosure is the use of one or more control devices and methods to control the amount of energy dissipated by a braking compressor or other energy dissipating braking device. As can be appreciated, it may be desirable to dissipate large or small amounts of energy depending on the speed of the vehicle and the desired braking force. Hard braking at high speeds while going down hill can require large amounts of braking energy to be dissipated by an engine braking system in addition to that dissipated by the foundation braking system. Light braking at low speeds can be provided by the foundation braking system or by engine braking. The latter may be preferred since it may save undue wear and tear on the foundation braking system.

Another advantage of these control methods is that they may be used to route some of the engine braking energy to energy storage devices rather than simply dissipating this energy.

Such control devices disclosed herein include (1) a continuously variable transmission (“CVT”); (2) an electrical generator and an optional thermal storage device; (3) an eddy current clutch; and (4) a fluid pump system. The control devices can be operated automatically by a computer to provide the desired amount of braking force, for example, in response to the vehicle operator depressing a brake petal. In the case of the electrical generator or fluid pump system, these may be used both to dissipate braking energy as well as control the amounts and rate of braking energy dissipation.

Additional innovations disclosed herein include vehicle braking systems that utilize some or all the braking features to recoup a portion of braking energy available with either or both of a hybrid transmission and an energy dissipating braking apparatus.

In the present disclosure relating to a braking compressor, attention will be focused on the design of subsonic compressors. The braking compressor of the present disclosure can be a single centrifugal compressor, a two-stage centrifugal compressor, or a centrifugal and axial compressor combination. As an example, consider a vehicle with a 375 kW engine. In order to provide significant engine braking, a braking compressor would have to dissipate power in the range of about 150 kW to about 400 kW. To achieve this range of power dissipation in a compact apparatus, a compressor system capable of a pressure ratio in the range of about 6:1 to about 12:1 would normally be required.

Gear Configurations and Ratios

FIG. 5 illustrates an example, in end view, of how a braking compressor or other engine braking apparatus can be geared for the configuration of FIG. 3 (braking compressor associated with the free power turbine). As shown in FIG. 5 a, high speed pinion 43 drives a high speed bull gear 41 where high speed pinion 43 is attached to the shaft of a free power turbine. The typical reduction between high speed pinion 43 and high speed bull gear 41 is commonly in the range of about 2:1 to about 10:1 and more commonly in the range of about 4:1 to about 7:1. Another pinion 45 is attached to high speed bull gear 41 and drives low speed bull gear 42. The typical reduction between high speed bull gear 41 and low speed bull gear 42 is commonly in the range of about 2:1 to about 10:1 and more commonly in the range of about 4:1 to about 7:1. A shaft 46 attached to low speed bull gear 42 is connected to a clutch and gear box as described in FIG. 6. A second high speed pinion 44 drives a power take-off shaft which operates the braking compressor or other dissipating apparatus of the present disclosure. FIG. 5 b illustrates the gear engagement of pinions 43 and 44 with bull gear 41. Similar tooth engagement applies to pinion 45 and low speed bull gear 42. As can be appreciated the specific gear configuration may be any type of gear such as, for example, spur, helical, double helical, bevel or hypoid gears.

In the following, the present disclosure is illustrated for a braking compressor. As can be appreciated, the same gearing and control methods can be applied to other energy dissipating devices such, as for example, an electrical generator or a fluid pump.

FIG. 6 illustrates an example, in plan view, of how a prior art braking compressor (that is a braking compressor with an inlet and/or outlet air flow control device) may be operated with a mechanical transmission and a gas turbine engine. This figure shows free power turbine 8 with its output shaft 61 driving a transmission defined by boundary 9 (dashed lines) that transmits power from output shaft 61 to drive shaft 52. Transmission components located inside a bell housing are contained to the left of boundary 10 (dash-dot line) and extending to the left edge of transmission boundary 9. Free power turbine output shaft 61 includes a high speed pinion 43 which drives a high speed bull gear 41. Shaft 64 is attached to high speed bull gear 41 and includes a pinion 45 that drives low speed bull gear 42. Shaft 65 is attached to low speed bull gear 42 and to clutch assembly 51. Shaft 66 attaches the other side of clutch assembly 51 to gearbox 50 which contains switchable gear sets that can provide multiple gear ratios, with the ability to switch between them as speed varies. This switching may be done manually or automatically and may include the ability to provide forward and reverse directional control. Gearbox 50 transmits power to drive shaft 52 which, in turn, is attached to one or more differentials 53. Differentials 53 drive axles 54 which power wheels 55. This figure is an example of how a gas turbine engine can be used with a mechanical transmission to propel a vehicle. As part of the present disclosure, a power take-off pinion 44 is attached to shaft 63 which is attached to a second clutch assembly 11. Shaft 62 is attached to the other side of clutch assembly 11 and to braking compressor 12. As can be appreciated, braking compressor 12 can be replaced with any dissipating apparatus such as, for example, an electrical motor that dissipates energy at the required power. As can be further appreciated, the energy from the dissipating apparatus can be utilized for useful purposes. For example, if the dissipating apparatus is a compressor, it can be used to charge a pneumatic energy storage apparatus which can be used to energize a pneumatic braking system. Alternately, for example, if the dissipating apparatus is an electrical motor, it can be used to charge an electrical energy storage system such as a battery pack, a capacitor bank or a system of flywheels.

In normal driving mode, clutch assembly 51 is engaged so that power from free power turbine 8 is transmitted to wheels 55 by the drive train. Clutch assembly 51 may be disengaged when the engine is idling or when the engine is turned off In normal driving mode, clutch assembly 11 is usually disengaged. If free power turbine 8 is sensed to be over-speeding, then clutch assembly 11 may be engaged to control free power turbine over-speeding by extracting energy. Over-speeding can occur when the load on the free power turbine is abruptly decreased or removed.

In braking mode, clutch assembly 51 may be engaged or disengaged. In braking mode, when clutch assembly 51 is disengaged, clutch assembly 11 may be engaged to prevent free power turbine from over-speeding which can occur when the its load is abruptly removed. In braking mode, when clutch assembly 51 is engaged, clutch assembly 11 may be engaged to transmit braking energy back through the drive train to the braking compressor, thereby providing engine braking in the same way that a Jacobs brake provides additional braking for a reciprocating engine.

It was stated previously that clutch assembly 11 may be optional. With clutch assembly 11 disengaged, there is no parasitic load on the free power turbine when braking compressor 12 is not required. It is possible to eliminate clutch assembly 11 and use the outlet nozzle of the braking compressor to control braking. When not required, the outlet nozzle can be opened fully so that there is substantially no load and therefore substantially no energy extracted by the braking compressor. The rotor or rotors of the braking compressor apparatus can be allowed to rotate with substantially no pressure differential until braking is required and this will result in a small parasitic load on the free power turbine. For engine braking or control of free power turbine over-speed, the outlet nozzle on the braking compressor can be closed to extract energy at a selected rate with or without clutch assembly 11 as part of the system. Eliminating clutch assembly 11 would result in a small parasitic load to the vehicles engine. Thus, if overall engine and transmission efficiency are to be optimized, then retaining clutch assembly 11 would be preferable, especially if the vehicle is a long haul vehicle.

As can be appreciated, a braking compressor can also be used in conjunction with a hybrid transmission or an all electric transmission. A hybrid transmission is considered to be a transmission that can be operated as an electrical transmission or a mechanical transmission, depending on vehicle speed. For example, the free power turbine can drive an electrical generator and the electrical generator can drive a traction motor. At higher speeds, the electrical generator and traction motor can be locked up so that the transmission becomes a purely mechanical transmission. For any type of transmission, free power turbine 8 can be connected to a pinion and bull gear arrangement such as pinions 43, 44 and bull gear 41 to utilize a braking compressor for engine braking and free power turbine over-speed control.

As can be appreciated, the amount of braking force supplied by either or both of an inlet and outlet vanes of the braking compressor may be controlled automatically by an appropriate control algorithm which is responsive to the data from various shaft rpms, free power turbine rpms and brake pedal force.

As will be described in FIGS. 7,9,12 and 16, FIG. 6 is the basic transmission and gearing configuration for embodiments wherein various innovative control apparatuses are used to modulate braking compressor performance.

If a braking compressor is used, the output air from the braking compressor can be discharged to the atmosphere, or it can be used to charge a pneumatic storage tank, or it can be used for quenching hot recuperator gases to assist in engine turndown. In the latter case, as the vehicle is braking, the cool output air from the braking compressor can be injected into the exhaust flow upstream of the entrance to the hot side of the recuperator (see FIG. 1 for an example of a recuperated gas turbine engine). This will rapidly lower the temperature of the hot side recuperator air and consequently reduce the energy transferred from the recuperator hot side to the recuperator cold side. Since the rate of fuel injection is usually reduced during braking, the combined effect of fuel reduction and lowered energy transfer through the recuperator will more rapidly reduce the power output of the combustor. The net effect will be to more rapidly slow down the downstream turbines, including the free power turbine.

Control Using a Continuously Variable Transmission (“CVT”)

FIG. 7 illustrates an example, in plan view, of how a braking compressor can be controlled using a CVT. Depending on the rpm capability of the CVT, the CVT may be connected to the braking compressor via an increasing gear. The CVT is connected to the power train by a clutch assembly. As is well-known, a CVT has a low gear ratio and a high gear ratio with infinitely many ratios in-between. The advantage of a CVT is the ability to keep the braking compressor rpms in their desired range for all braking conditions. The free power turbine, the apparatuses contained within the transmission, the drive shaft, differential and wheels are the same as those of FIG. 6. As part of the present disclosure, a power take-off pinion 44 is attached to shaft 63 which is attached to a second clutch assembly 11. Shaft 62 is attached to the other side of clutch assembly 11 and to the input side of CVT. The output side of CVT 15 is shown attached to an increasing gearbox 16 by shaft 67. Gearbox 16 is then attached to a braking compressor 12 by shaft 68. If the rpm range of the CVT is high enough, increasing gearbox 16 may not be required. As can be appreciated, braking compressor 12 can be replaced with any dissipating apparatus such as an electrical motor that dissipates energy at the required power level. As can be further appreciated, the energy from the dissipating apparatus can be utilized for useful purposes. For example, if the dissipating apparatus is a compressor, it can be used to charge a pneumatic energy storage apparatus which can be used to energize a pneumatic braking system. Alternately, for example, if the dissipating apparatus is an electrical motor, it can be used to charge an electrical energy storage system such as a battery pack, a capacitor bank or a system of flywheels.

In normal driving mode, clutch assembly 51 is engaged so that power from free power turbine 8 is transmitted to wheels 55 by the drive train. Clutch assembly 51 may be disengaged when the engine is idling or when the engine is turned off. In normal driving mode, clutch assembly 11 is usually disengaged. If free power turbine 8 is sensed to be over-speeding, then clutch assembly 11 may be engaged to control free power turbine over-speeding by extracting energy. Over-speeding can occur when the load on the free power turbine is abruptly decreased or removed. The CVT may be controlled to provide a light to heavy braking action by continuously varying the CVT gear ratio as described below.

In braking mode, clutch assembly 51 may be engaged or disengaged. In braking mode, when clutch assembly 51 is disengaged, clutch assembly 11 may be engaged to prevent free power turbine from over-speeding which can occur when the load is abruptly removed. In braking mode, when clutch assembly 51 is engaged, clutch assembly 11 may be engaged to transmit braking energy back through the drive train to the braking compressor via CVT 15, thereby providing a continuously variable engine braking in the same way that a Jacobs brake provides such braking for a reciprocating engine. The increasing gearbox may be optional and is typically used to provide higher compressor rpms and additional braking energy at low speeds.

Consider the schematic of FIG. 7 for the example of a gas turbine engine with an approximate peak output shaft power of about 350 kW. Such an engine might be operated at a high speed road power output of about 175 kW to about 275 kW. Typical free power turbine 8 rotor speed is in the range of about 80,000 to about 120,000 rpms. The pinion 43 to bull gear 41 gear ratio may be approximately 7:1 so that shaft 64 rotates in the range of about 10,000 to about 12,500 rpms. The pinion 45 to bull gear 42 gear ratio may be also approximately 7:1 so that shaft 65 and 66 when engaged rotates in the range of about 1,250 to about 1,560 rpms.

A CVT has a low gear ratio and a high gear ratio with infinitely many ratios in-between. For example, the lowest gear ratio may be 0.2:1 and the highest about 1.2:1. Thus the total range of gear ratios is about 6:1 from lowest to highest.

Consider a large vehicle at a speed of about 70 mph. The wheel axles 54 would rotate at 588 rpms for a 40-inch wheel diameter. With a differential gear ratio of 3, the main drive shaft 52 would rotate at 1,765 rpms. In high gear (1:1), shaft 64 would rotate at 12,353 rpms and shaft 62 at 86,471 rpms. If CVT 15 is in its lowest gear setting (0.2:1), then shaft 67 rotates at 17,394 rpms. If gear box 16 is set at 2:1, then the braking compressor would rotate at 34,588 rpms which would be considered light braking.

Now consider the same vehicle at a speed of about 10 mph. The wheel axles 54 would rotate at 84 rpms. The main drive shaft 52 would rotate at 252 rpms. In low gear (4:1), shaft 64 would rotate at 7,059 rpms and shaft 62 at 49,412 rpms. If CVT 15 is in its highest gear setting (1.2:1), then shaft 67 rotates at 59,294 rpms. If gear box 16 is set at 2:1, then the braking compressor would rotate at 118,589 rpms which would be considered heavy braking.

As can be appreciated, the gear settings may be controlled automatically by an appropriate control algorithm which is responsive to the data from various shaft rpms, free power turbine rpms and brake pedal force.

Control Using a Electrical Generator and Thermal Energy Storage Module

FIG. 8 illustrates in detail a braking compressor combined with a high speed electrical generator and thermal energy storage module. Shaft 67 rotates generator 19 which rotates shaft 68. Shaft 68 drives braking compressor 12 which has an air inlet path 101 and a compressed air output path 102. A thermal energy storage (“TES”) unit 72 is located in the discharge high-velocity air stream on the output side of braking compressor 12. Such a thermal energy storage device is described in U.S. patent application Ser. No. 12/777,916, entitled “Gas Turbine Energy Storage and Conversion System” which is incorporated herein by reference. Electrical generator 19 may be engaged to generate a selected amount of electrical energy by means of its control excitation to provide a selected amount of retardation force on the rpms of shafts 67 and 68. The electrical current output by generator 19 is carried via conductive path 77 and dissipated in TES unit 72 where a grid of wires is heated via Joule heating. The heat energy generated in the wire grid is carried away in the high velocity output air stream 102. As can be appreciated, the electrical energy generated by generator 19 can be re-directed to charge a battery or to a TES device located inside the pressure boundary of the gas turbine engine as described in U.S. patent application Ser. No. 12/777,916. The system described in FIG. 8 can provide a higher retarding force than the compressor alone and can provide control of the rpms and hence the amount of energy dissipated by braking compressor 12. Electrical generator 19 may be a brushless alternator to avoid the need for rotating electrical connections.

In this example, the discharge air from braking compressor 12 is used to dissipate heat stored in TES unit 72. As can be appreciated, the electrical energy from generator 19 may be dissipated by other means such as, for example, a dynamic braking grid located elsewhere on the vehicle and whose energy can be dissipated by air flow past the vehicle.

In the configuration of FIG. 9, the generator 19, when excited, can be operated to apply additional braking torque to shaft 67. The generator can also be driven in parallel to braking compressor 12 as described for another control device in FIG. 16.

FIG. 9 illustrates an example, in plan view, of how a braking compressor can be controlled using a high speed generator and thermal energy storage module. Depending on the rpm capability of the high speed generator, the high speed generator may be connected to the braking compressor via an increasing gear. The high speed generator is connected to the power train by a clutch assembly.

In the example of FIG. 9, an electric generator that uses field coils rather than permanent magnets is depicted. This type of generator requires a current to be present in the field coils for the device to be able to produce a retarding torque. If the field coils are not powered, the rotor in the generator can spin without producing any output electrical energy. As is well-known, this type of high speed generator has a wide range of electrical output depending on the level of excitation applied. The advantage of the high speed generator is its ability to increase the amount of braking force by generating while the braking compressor is operative. The free power turbine, the apparatuses contained within the transmission, the drive shaft, differential and wheels are the same as those of FIG. 6. As part of the present disclosure, a power take-off pinion 44 is attached to shaft 63 which is attached to a second clutch assembly 11. Shaft 62 is attached to the other side of clutch assembly 11 and to the input side of the high speed generator 19. The output side of high speed generator 19 is attached to a braking compressor 12 by shaft 68. As can be appreciated, the electrical output of the high speed generator 19 can be utilized for useful purposes. For example, electrical output of the high speed generator 19 can be used to charge an electrical energy storage system such as a battery pack, a capacitor bank or a system of flywheels.

In normal driving mode, clutch assembly 51 is engaged so that power from free power turbine 8 is transmitted to wheels 55 by the drive train. Clutch assembly 51 may be disengaged when the engine is idling or when the engine is turned off In normal driving mode, clutch assembly 11 is usually disengaged. If free power turbine 8 is sensed to be over-speeding, then clutch assembly 11 may be engaged to control free power turbine over-speeding by extracting energy. Over-speeding can occur when the load on the free power turbine is abruptly decreased or removed. The high speed generator 19 may be controlled to provide a light to heavy braking action by continuously varying the applied excitation.

In braking mode, clutch assembly 51 may be engaged or disengaged. In braking mode, when clutch assembly 51 is disengaged, clutch assembly 11 may be engaged to prevent free power turbine from over-speeding which can occur when the load is abruptly removed. In braking mode, when clutch assembly 51 is engaged, clutch assembly 11 may be engaged to transmit braking energy back through the drive train to the braking compressor via the high speed generator 19, thereby providing a continuously variable engine braking force in the same way that a Jacobs brake provides such braking for a reciprocating engine. An increasing gearbox between the high speed generator and the braking compressor may be used if the rpm capability of the high speed generator is too low.

As can be appreciated, the thermal energy storage module need not be present, especially if the electrical output of the high speed generator is used to provide auxiliary power, charge an energy storage system or if a dynamic braking grid already exists.

As can be appreciated, the amount of excitation applied to the electrical generator may be controlled automatically by an appropriate control algorithm which is responsive to the data from various shaft rpms, free power turbine rpms and brake pedal force.

As can be further appreciated, the braking compressor 12 can be eliminated and generator 19 can be used as the energy dissipation device. Control of braking power and energy would be by the amount of excitation applied to the generator. The output of the generator can be re-directed to charge a battery or to a TES device located inside the pressure boundary of the gas turbine engine or to a dynamic braking grid.

Control Using an Eddy Current Clutch Assembly

Eddy current clutches are well-known. The following is an innovative approach to an eddy current clutch based on a brushless alternator. A brushless alternator is composed of two alternators built end-to-end on one shaft. FIG. 10 illustrates an example of a brushless eddy current clutch assembly with DC excitation. This is an apparatus that can be used to provide a clutching function between a vehicle's drive train and a braking apparatus such as a braking compressor, in order to activate an engine braking function. For example, the brushless eddy current clutch assembly of FIG. 10 can be the clutch assembly 11 in FIG. 6. The control function of the brushless eddy current clutch assembly of FIG. 10 can therefore be understood in relation to the engine braking role of clutch assembly 11 in FIG. 6. As shown in FIG. 10, the input is shaft 1 which rotates when the free power turbine (such as shown in FIG. 6) rotates. Input shaft 1 is mechanically connected to exciter armature 3 which, in turn is mechanically connected to diode board 4 which is, in turn, mechanically connected main field coil 5. Exciter armature 3 is electrically connected to diode board 4 by 3 phase AC wires 12 and diode board 4 is electrically connected to main field coil 5 by DC wires 13. Exciter armature 3, diode board 4 and main field coil 5 all rotate when input shaft 1 rotates. When there is no excitation field in exciter field coil 2, then there is no field generated in main field coil 5 and the main armature 6 does not rotate. Since main armature 6 is mechanically connected to housing 10 which is mechanically connected to output shaft 7, there is no rotation of output shaft 7 when there is no exciter field. Exciter field coil 2 is mechanically mounted in housing 8 which is fixed in position with respect to the free power turbine. The exciter field can be activated by variable DC control system 11 which can provide a selected amount of DC current to stationary exciter field coil 2.

As the DC current in exciter field coil 2 is increased, an AC current is induced in rotating exciter armature 3. This AC current is rectified in diode board 4 and causes a DC current in main field coil 5. The DC current in main field coil 5 then induces eddy currents in main armature 6. Main armature 6 may be a wound coil or it may be a solid block of conductor (for example aluminum which is an excellent conductor and is low density). The eddy currents induced in main armature 6 cause a rotational force in main armature 6 which tends rotate main armature 6 so as to reduce these eddy currents. As main armature 6 rotates, its housing 10 and hence output shaft 7 rotate with it. As the current in exciter field coil 2 is increased further, main armature 6 which is connected to housing 10 and output shaft 7 rotates faster and faster until it is rotating almost as fast as input shaft 1. Typically the output shaft can be caused to rotate within a few percent of the rotation speed of the input shaft. Thus by varying the DC control 11, the slippage between the input and output shaft can be varied between full disengagement to almost complete lock-up (1 or 2% slippage).

It is also possible to reverse the generator of FIG. 10 so that shaft 7 is the input shaft from the drive train and shaft 1 is the output shaft to the braking compressor. FIG. 11 illustrates an example of a brushless eddy current clutch assembly with AC excitation. The mechanical and electrical connections are the same as those of FIG. 10. However, the DC excitation control is replaced by an AC excitation control. When there is no excitation current, then only shaft 7, housing 10 and main armature 6 rotate. When an AC field in exciter field is applied in coil 2, this will induce a field in exciter armature 3 and this will be rectified by diode board 4 and create a DC current in main field coil 5. The rotation of main armature 6 will then cause eddy currents to flow in main armature 6 and this will cause a rotational torque in main field coil 5 which will rotate shaft 1. Once the rotation of shaft 1 begins, the AC input to exciter field coil 3 can be controlled by an appropriate algorithm to regulate the degree of clutch engagement required.

FIG. 12 illustrates an example, in plan view, of how a braking compressor can be controlled using an eddy current clutch assembly. Depending on the rpm capability of the eddy current clutch assembly, one side of the eddy current clutch is connected to the braking compressor via an increasing gear. The other side of the eddy current clutch is connected to the power train. As is well-known, an eddy current clutch assembly has a continuously variable range of clutching action from zero engagement to almost totally locked (a small amount of residual slippage in the range of about 1 or 2% from being fully locked), depending on the current controlling the clutch. The advantage of an eddy current clutch assembly is that it performs the function of a clutch and as well as a control device to keep the braking compressor rpms in their desired range for all braking conditions. The free power turbine, the apparatuses contained within the transmission, the drive shaft, differential and wheels are the same as those of FIG. 6. As part of the present disclosure, a power take-off pinion 44 is attached to shaft 63 which is attached to eddy current clutch assembly 11. Shaft 67 is attached to the other side of eddy current clutch assembly 11 and to the input side of an increasing gearbox 16. Gearbox 16 is then attached to a braking compressor 12 by shaft 68. As can be appreciated, braking compressor 12 can be replaced with any dissipating apparatus such as an electrical motor that dissipates energy at the required power. As can be further appreciated, the energy from the dissipating apparatus can be utilized for useful purposes. For example, if the dissipating apparatus is a compressor, it can be used to charge a pneumatic energy storage apparatus which can be used to energize a pneumatic braking system. Alternately, for example, if the dissipating apparatus is an electrical motor, it can be used to charge an electrical energy storage system such as a battery pack, a capacitor bank or a system of flywheels.

In normal driving mode, clutch assembly 51 is engaged so that power from free power turbine 8 is transmitted to wheels 55 by the drive train. Clutch assembly 51 may be disengaged when the engine is idling or when the engine is turned off. In normal driving mode, eddy current clutch assembly 11 is usually fully disengaged. If free power turbine 8 is sensed to be over-speeding, then eddy current clutch assembly 11 may be partially or fully engaged to control free power turbine over-speeding by extracting energy. Over-speeding can occur when the load on the free power turbine is abruptly decreased or removed. The eddy current clutch assembly may be controlled to provide a light to heavy braking action by continuously varying the current to the eddy current clutch assembly.

In braking mode, clutch assembly 51 may be engaged or disengaged. In braking mode, when clutch assembly 51 is disengaged, eddy current clutch assembly 11 may be engaged to prevent free power turbine from over-speeding which can occur when the load is abruptly removed. In braking mode, when clutch assembly 51 is engaged, eddy current clutch assembly 11 may be fully or partially engaged to transmit braking energy to the braking compressor, thereby providing a continuously variable engine braking in the same way that a Jacobs brake provides such braking for a reciprocating engine. The increasing gearbox may be optional and is typically used to provide higher compressor rpms and additional braking energy at low speeds, depending on the rpm range of the eddy current clutch system.

As can be appreciated, the degree of engagement of the eddy current clutch assembly may be controlled automatically by an appropriate control algorithm which is responsive to the data from various shaft rpms, free power turbine rpms and brake pedal force.

Control Using a Fluid Pump Circuit

FIG. 13 illustrates a fluid pump circuit for dissipating energy for the fluid pump described in FIG. 16. This figure shows an oil pump 1 whose throughput is controlled by restrictor valve 2. The resistance to pump 1 is provided by restrictor valve 2 which, as it is controlled to restrict the flow of oil, can increase the temperature of the oil and cause the pump to work harder. The work done by the pump and the heating of the oil are the mechanisms for energy dissipation of the pump system. As is appreciated, the viscosity of the heated oil will in general will be reduced and the restrictor valve will have to be closed further to compensate for this effect while increasing the work done by the pump.

The heated oil is subsequently cooled in heat exchanger 3 and returned to oil reservoir 4. Thus by controlling the flow restriction provided by valve 2, the amount of work required by pump 1 can be controlled. The advantage of this system, in addition to providing additional engine braking power and/or controlling the rpms of the braking compressor, is that it can be formed by components already existing in the engine's oil lubrication system. For example, the heat exchanger for cooling the oil and the reservoir can be pre-existing components of an engine lubricating system.

FIG. 14 is an isometric view of prior art planetary gear set. This figure illustrates a typical three planet gear planetary gear set. In the application described in FIG. 16, the braking compressor is driven by the high-speed sun pinion. The input to the planetary gear is from the vehicle's transmission through a low speed bull gear and pinion gear as described in FIG. 16. Referring to FIG. 15, the input to the planetary gear set can be from the planet carrier or the ring (orbit) gear. The pump can be driven by the planet carrier or the ring (orbit) gear while the braking compressor is preferably driven by the sun pinion. As can be appreciated, a planetary gear offers a variety of options depending on the rpms required by the pump and braking compressor.

FIG. 15 illustrates an example of how a planetary gear system can be used for control of a braking compressor. FIG. 15 a shows a head-on view of the output side of a planetary gear system. Sun gear 1 is rotated by four planet gears 2, all of which are attached to planet carrier 5. Planet gears 2 also engage teeth on the inside of ring gear 3. Ring gear 3 also has teeth on its outer side and these teeth engage spur gear 11. The output shaft of sun gear 1 drives a braking compressor as described in FIG. 16. The output shaft of spur gear 11 drives a fluid pump (or electrical generator or eddy current brake) also as described in FIG. 16. FIG. 15 b shows a side view of a planetary gear system. Low speed input shaft 6 rotates planet carrier 5 which rotates planet gears 2. Planet gears 2 rotate sun gear 1 which drives output shaft 7 which is connected to the braking compressor as described in FIG. 16. Planet gears 2 engage the inside of ring gear 3. Spur gear 11 engages the outside of ring gear 3. The shaft of spur gear 11 drives shaft 8 which is connected to a fluid pump, electrical generator, eddy current brake or any other suitable apparatus that can apply a variable torque to ring gear 3.

FIG. 16 illustrates an example, in plan view, of how a braking compressor can be controlled using a fluid pump and planetary gear system. A fluid pump system 49 is connected to a pinion gear 58 by shaft 59. Pinion gear 58 engages with gear teeth on the outside of the ring gear of a planetary gear system 48. This setup was described in more detail in FIG. 15. As can be appreciated, fluid pump 49 may be an electrical generator or an eddy current brake for example. The function fluid pump 49 is to apply from zero to a maximum torque on planetary ring gear. If fluid pump 49 applies no torque to the ring gear, then the ring gear will free wheel and the sun gear will rotate slowly since the input shaft 62 will rotate the planet carrier which will turn the planetary gears at their minimum rotational speed. If fluid pump 49 applies maximum torque to the ring gear, then the ring gear will tend to rotate slowly or not at all and the sun gear will rotate rapidly since the input shaft 62 will rotate the planet carrier and the planet gears will turn at their maximum rotational speed. As can be appreciated, the rotation of the fluid pump shaft 59 can be set up so that it can reverse the rotational direction of ring gear 58 which will cause the rotational speed of sun gear and shaft 68 to increase further. The free power turbine, the apparatuses contained within the transmission, the drive shaft, differential and wheels are the same as those of FIG. 6. As part of the present disclosure, a power take-off pinion 44 is driven by low speed bull gear 42. Pinion 44 is attached to shaft 63 which is attached to a second clutch assembly 11. Shaft 62 is attached to the other side of clutch assembly 11 and to the input side of the planetary gear system 48. The input side of planetary gear system 48 rotates the planetary carrier as described in more detail in FIG. 15. In this configuration, the output of the planetary gear set is the sun pinion which drives shaft 6 which is, in turn, connected to braking compressor 12.

In normal driving mode, clutch assembly 51 is engaged so that power from free power turbine 8 is transmitted to wheels 55 by the drive train. Clutch assembly 51 may be disengaged to idle the engine or when the engine is turned off. In normal driving mode, clutch assembly 11 is usually disengaged. If free power turbine 8 is sensed to be over-speeding, then clutch assembly 11 may be engaged to control free power turbine over-speeding by extracting energy. Over-speeding can occur when the load on the free power turbine is abruptly decreased or removed. The fluid pump 49 may be controlled to provide a light to heavy braking action by continuously varying the torque it applies to the outside of the ring gear of the planetary gear system.

In braking mode, clutch assembly 51 may be engaged or disengaged. In braking mode, when clutch assembly 51 is disengaged, clutch assembly 11 may be engaged to prevent free power turbine from over-speeding which can occur when the load is abruptly removed. In braking mode, when clutch assembly 51 is engaged, clutch assembly 11 may be engaged to transmit braking energy back through the drive train to the braking compressor, with control of the braking compressor rotational speed being provided by the amount of torque applied to the ring gear of the planetary gear system 48. This system thereby provides a continuously variable engine braking in the same way that a Jacobs brake provides such braking for a reciprocating engine. The drive input to the planetary gear set is determined by the desired gear ratio to match the rpm range of low speed bull gear 42 with the rpm range of the sun pinion.

Consider an example of a planetary gear set with a sun pinion having 30 teeth, four planet gears having 15 teeth each, and the ring gear having 150 teeth on its inner ring. When the ring gear is free wheeling, the sun gear rotates at 6 times the rotational speed of the planet carrier. When the ring gear is fixed and stationary, the sun gear rotates at 3 times the rotational speed of the planet carrier. Thus by controlling the torque applied to the outside of the ring gear by the fluid pump, the rotational speed of the braking compressor can be varied by a factor of 2 which means its retarding force can be varied by the square of its rotational speed or by a factor of 4.

A particular advantage of the configuration of FIG. 16 is that the various gears in the transmission and the planetary gears require lubrication and cooling. The oil pump can be used to circulate oil in the vehicle's transmission gears as well as in the planetary gears. The air expanded from the braking compressor can be used to cool the planetary gear set as well as remove the heat coming off the heat exchanger in the fluid pump circuit. When the engine braking system is working, the resistance provided by the oil pump is controlled by a restrictor valve as described in FIG. 12. This heats the oil beyond its normal operating temperature and the air expanded from the braking compressor can be used to provide cooling via the heat exchanger of FIG. 12 to maintain the oil at its desired operating temperature. In this way, the engine braking system of FIG. 16 can be configured to work with other engine lubrication and cooling systems that are existing sub-systems of the basic engine.

As can be appreciated, the degree of engagement of the fluid pump applied to the outside of the ring gear be controlled automatically by an appropriate control algorithm which is responsive to the data from various shaft rpms, free power turbine rpms and brake pedal force.

As can be further appreciated, the braking compressor 12 can be eliminated and fluid pump 49 can be used as the energy dissipation device. Control of braking power and energy would be by the restrictor valve in the fluid circuit. As noted previously, the work done by the pump and the heating of the oil are the mechanisms for energy dissipation of the pump system.

Braking Systems for a Gas Turbine Engine

FIG. 17 is a schematic of a hybrid braking system for a gas turbine engine. This figure illustrates a braking system for the example of a gas turbine engine and braking compressor such as shown in FIG. 3 with simple gearing for the braking as shown in FIG. 6. As can be appreciated, other engine braking control methods, such as shown in FIGS. 7, 9, 12 and 16 may be used. The braking system shown in FIG. 17 includes a hybrid transmission 44 which can provide electric propulsive power transmission at low speeds and direct mechanical propulsive power transmission at higher speeds. Such hybrid transmissions are known and described, for example, in U.S. patent application Ser. No. 12/777,916 entitled “Gas Turbine Energy Storage and Conversion System” and is incorporated herein by reference.

In normal driving mode, clutch assembly 43 is engaged so that power from free power turbine 8 is transmitted to the vehicles wheels by the drive train. Clutch assembly 43 may be disengaged when the engine is idling or when the engine is turned off. In normal driving mode, clutch assembly 13 is usually disengaged. If free power turbine 8 is sensed to be over-speeding, then clutch assembly 13 may be engaged to control free power turbine over-speeding by extracting energy by means of braking compressor 12. The compressed air provided by braking compressor 12 may be discarded or it may be used to pressurize air reservoir 46 which is part of a pneumatic braking system 45 for the vehicle. The capability to provide compressed air as just described is applicable to either a mechanical, hybrid or all-electrical transmission.

In braking mode, clutch assembly 43 may be engaged or disengaged. In braking mode, when clutch assembly 43 is disengaged, clutch assembly 13 may be engaged to prevent free power turbine from over-speeding which can occur when the its load is abruptly removed. In braking mode, when assemblies 43 and 13 are engaged, energy is transmitted to the braking compressor, thereby providing engine braking in the same way that a Jacobs brake provides such braking for a reciprocating engine. As can be appreciated, any of the control devices disclosed herein (continuously variable transmission; an electrical generator and a thermal storage device; an eddy current clutch assembly; a fluid pump system; or any combination of these) may be included with the braking compressor for control purposes. If a hybrid or electrical transmission is used, then electrical energy generated by braking may be used to charge a battery or battery pack 12; heat a thermal storage element 13; operate pneumatic pump 47; and/or operate a control motor 10 on the high pressure spool (comprised of compressor 3 and turbine 6) or low the pressure spool (comprised of compressor 1 and turbine 7). Such a thermal energy storage device is disclosed in U.S. patent application Ser. No. 12/777, 916 entitled “Gas Turbine Energy Storage and Conversion System”. Such a turbine spool control motor is disclosed in U.S. patent application Ser. No. 13/175,564 entitled “Improved Multi-spool Intercooled Recuperated Gas Turbine” and is incorporated herein by reference.

FIG. 18 is a schematic of a first alternate hybrid braking system for a gas turbine engine. This figure illustrates a braking system for the example of a gas turbine engine and braking compressor such as shown in FIG. 3. As can be appreciated, other engine braking control methods, such as shown in FIGS. 7, 9, 12 and 16 may be used. The braking system shown in FIG. 18 includes a hybrid transmission 44 which can provide electric propulsion power transmission at low speeds and direct mechanical propulsive power transmission at higher speeds.

In normal driving mode, clutch assembly 43 is engaged so that power from free power turbine 8 is transmitted to the vehicles wheels by the drive train. Clutch assembly 43 may be disengaged when the engine is idling or when the engine is turned off. In normal driving mode, clutch assembly 13 is usually disengaged. If free power turbine 8 is sensed to be over-speeding, then clutch assembly 13 may be engaged to control free power turbine over-speeding by extracting energy by means of braking compressor 12. The compressed air provided by braking compressor 12 may be discarded or it may be used to pressurize air reservoir 46 which is part of a pneumatic braking system 45 for the vehicle. The capability to provide compressed air as just described is applicable to either a mechanical, hybrid or all-electrical transmission.

In braking mode, clutch assembly 43 may be engaged or disengaged. In braking mode, when clutch assembly 43 is disengaged, clutch assembly 13 may be engaged to prevent free power turbine from over-speeding which can occur when the load is abruptly removed. In braking mode, when clutch assemblies 43 and 13 are engaged, energy is transmitted to the braking compressor, thereby providing engine braking in the same way that a Jacobs brake provides such braking for a reciprocating engine. This configuration shows a control system described previously in FIG. 7 comprised of (a continuously variable transmission 25 and gearbox 26). If a hybrid or electrical transmission is used, then electrical energy generated by braking may be used to charge a battery or battery pack 12; heat a thermal storage element 13; operate pneumatic pump 47; and/or operate a control motor 10 on the high pressure spool (comprised of compressor 3 and turbine 6) or low the pressure spool (comprised of compressor 1 and turbine 7).

FIG. 19 is a schematic of a second alternate hybrid braking system for a gas turbine engine. This figure illustrates a braking system for the example of a gas turbine engine and braking compressor such as shown in FIG. 3. As can be appreciated, other braking configurations, such as shown in FIGS. 7, 9, 12 and 16 may be used. The braking system shown in FIG. 19 includes a hybrid transmission 44 which can provide electric propulsion power transmission at low speeds and direct mechanical propulsive power transmission at higher speeds.

In normal driving mode, clutch assembly 43 is engaged so that power from free power turbine 8 is transmitted to the vehicles wheels by the drive train. Clutch assembly 43 may be disengaged when the engine is idling or when the engine is turned off In normal driving mode, eddy current clutch assembly 25 is usually disengaged. If free power turbine 8 is sensed to be over-speeding, then eddy current clutch assembly 25 may be engaged to control free power turbine over-speeding by extracting energy by means of braking compressor 12. The compressed air provided by braking compressor 12 may be discarded or it may be used to pressurize air reservoir 46 which is part of a pneumatic braking system 45 for the vehicle. The capability to provide compressed air as just described is applicable to either a mechanical, hybrid or all-electrical transmission.

In braking mode, clutch assembly 43 may be engaged or disengaged. In braking mode, when clutch assembly 43 is disengaged, eddy current clutch assembly 25 may be engaged to prevent free power turbine from over-speeding which can occur when the its load is abruptly removed. In braking mode, when clutch assemblies 43 and 25 are engaged, energy is transmitted to the braking compressor, thereby providing engine braking in the same way that a Jacobs brake provides such braking for a reciprocating engine. This configuration shows a control system described previously in FIG. 12 (an eddy current clutch assembly 25 and gearbox 26). If a hybrid or electrical transmission is used, then electrical energy generated by braking may be used to charge a battery or battery pack 12; heat a thermal storage element 13; operate pneumatic pump 47; and/or operate a control motor 10 on the high pressure spool (comprised of compressor 3 and turbine 6) or low the pressure spool (comprised of compressor 1 and turbine 7). In addition, this regenerative braking system can also use electrical energy derived from braking to operate an electrolysis apparatus 51 which can utilize the electrical energy of braking to produce hydrogen from water stored in reservoir 52. The hydrogen produced can be stored as a compressed gas or fed directly into the inlet air stream of the gas turbine engine where it will react with available free oxygen to provide additional energy to the engine thereby allowing a reduction in primary fuel consumption. As can be appreciated, the electrolysis apparatus can be a fuel cell operated in reverse. As can also be appreciated, the electrolysis apparatus can be any other apparatus for producing a fuel using electrical energy from braking. For example, methane or methanol can be produced by a reforming and water shift apparatus from a supply of contaminated high carbon fuel such as dilbit (a mixture of bitumen and diluent that may be high in vanadium content).

In the braking systems of FIGS. 17, 18 and 19, other dissipating devices can be used in place of a braking compressor. These include an electrical generator or a fluid pump system. The braking compressor 12 can be eliminated and an electrical generator can be used as the energy dissipation device. Control of braking power and energy would be by the amount of excitation applied to the generator. The output of the generator can be re-directed to charge a battery or to a TES device located inside the pressure boundary of the gas turbine engine or to a dynamic braking grid. Alternately, the braking compressor 12 can be eliminated and fluid pump can be used as the energy dissipation device. Control of braking power and energy would be by the restrictor valve in the fluid circuit. As noted previously, the work done by the pump and the heating of the oil are the mechanisms for energy dissipation of the pump system.

FIGS. 20 a and 20 b is a flow chart for free power turbine over-speed control. Over-speed control can be implemented by an on-board computer that automatically interrogates the appropriate sensors, such as for example, free turbine rpms, the status or on/off state of the engine braking clutch and the transmission clutch, and control means for the braking device. In step 2001, the free power turbine control routine is initiated. In step 2002, the rpms of the free power are determined. In step 2003, if the rpms of the free power are not excessive, then the free power turbine control routine is terminated in step 2099. In step 2003, if the rpms of the free power are determined to be excessive, then the procedure moves to step 2004. If it is determined in step 2004 that the engine braking clutch is not engaged, then the engine braking clutch is engaged in step 2005 and the procedure moves to step 2006. If it is determined in step 2004 that the engine braking clutch is engaged, then the procedure moves directly to step 2006. If it is determined in step 2006 that the transmission clutch is engaged, then the transmission clutch is disengaged in step 2007 and the procedure moves to step 2008. The transmission clutch is disengaged since the rpms of the free power turbine would otherwise be controlled by the speed of the vehicle if the transmission clutch is engaged. The only effective way to reduce over-speed of the free power turbine is to disengage the transmission clutch so that the braking device can reduce the rpms of the free power turbine without have to slow down the entire vehicle.

In step 2008, the amount of engine braking to reduce the rpms of the free power turbine to acceptable levels is determined. In step 2009, the amount of engine braking force to reduce the rpms of the free power turbine to acceptable levels is applied by controlling the amount of engine braking force applied by the engine braking device. In step 2010, if the rpms of the free power turbine are no longer excessive, then the braking clutch is disengaged in step 2011 and the free power turbine control routine is terminated in step 2099. In step 2010, if the rpms of the free power are still determined to be excessive, then the procedure moves to back to step 2008 where the amount of engine braking to reduce the rpms of the free power turbine to acceptable levels is again determined.

FIGS. 21 a and 21 b is a flow chart for engine braking control. Engine braking control can be implemented by an on-board computer that automatically interrogates the appropriate sensors, such as for example, braking requests and free turbine rpms, the status of the engine braking clutch and the transmission clutch, and control means for the braking device. In step 2101, the engine braking control routine is initiated. In step 2102, any engine braking request is determined, for example, by sensing the motion of a brake pedal or by a command to implement engine braking. If there is no engine braking request or an engine braking is over ridden (for example by a GPS monitor sensing a restricted area for engine braking), the vehicle braking procedure is terminated in step 2109. If a valid engine braking is request is determined in step 2103 then the procedure moves to step 2104. If it is determined in step 2104 that the transmission clutch is not engaged, then the transmission clutch is engaged in step 22105 and the procedure moves to step 2106 where the engine braking clutch is engaged. If it is determined in step 2104 that the transmission clutch is engaged, then the procedure moves directly to step 2106 where the engine braking clutch is engaged. In step 2107, the amount of engine braking is determined. In step 2108, the selected amount of engine braking is applied. In step 2109, if it is determined that engine braking is no longer required, then the braking clutch is disengaged in step 2110 and the engine braking routine is terminated in step 2199. In step 2109, if it is determined that engine braking is still required, then the procedure moves to back to step 2107 where the amount of engine braking is again determined.

The exemplary systems and methods of this disclosure have been described in relation to preferred aspects, embodiments, and configurations. Modifications and alterations will occur to others upon a reading and understanding of the preceding detailed description. It is intended that the disclosure be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. To avoid unnecessarily obscuring the present disclosure, the preceding description omits a number of known structures and devices. This omission is not to be construed as a limitation of the scopes of the claims. Specific details are set forth to provide an understanding of the present disclosure. It should however be appreciated that the present disclosure may be practiced in a variety of ways beyond the specific detail set forth herein.

Furthermore, while the exemplary aspects, embodiments, and/or configurations illustrated herein show the various components of the system collocated, certain components of the system can be located remotely, at distant portions of a distributed network, such as a LAN and/or the Internet, or within a dedicated system. Thus, it should be appreciated, that the components of the system can be combined in to one or more devices or collocated.

Also, while the flowcharts have been discussed and illustrated in relation to a particular sequence of events, it should be appreciated that changes, additions, and omissions to this sequence can occur without materially affecting the operation of the disclosed embodiments, configuration, and aspects.

A number of variations and modifications of the disclosures can be used. As will be appreciated, it would be possible to provide for some features of the disclosures without providing others.

The present disclosure, in various embodiments, includes components, methods, processes, systems and/or apparatus substantially as depicted and described herein, including various embodiments, sub-combinations, and subsets thereof. Those of skill in the art will understand how to make and use the embodiments, aspects and configurations after understanding the present disclosure. The present disclosure, in various embodiments, includes providing devices and processes in the absence of items not depicted and/or described herein or in various embodiments hereof, including in the absence of such items as may have been used in previous devices or processes, for example for improving performance, achieving ease and\or reducing cost of implementation.

The foregoing discussion of the disclosure has been presented for purposes of illustration and description. The foregoing is not intended to limit the disclosure to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the disclosure are grouped together in one or more embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed disclosure requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate preferred embodiment of the disclosure.

Moreover though the description of the disclosure has included description of one or more embodiments and certain variations and modifications, other variations and modifications are within the scope of the disclosure, e.g., as may be within the skill and knowledge of those in the art, after understanding the present disclosure. It is intended to obtain rights which include alternative embodiments to the extent permitted, including alternate, interchangeable and/or equivalent structures, functions, ranges or steps to those claimed, whether or not such alternate, interchangeable and/or equivalent structures, functions, ranges or steps are disclosed herein, and without intending to publicly dedicate any patentable subject matter 

1. In a vehicle comprising a gas turbine engine and a transmission, the gas turbine engine comprising at least one turbo-compressor spool assembly, wherein the at least one turbo-compressor spool assembly comprises a compressor in mechanical communication with a turbine, the turbine outputting a gas, and a free power turbine in fluid communication with the turbine, the free power turbine being driven by the outputted gas, a system comprising: a braking device in mechanical communication with the free power turbine and the transmission to at least one of dissipate energy of the free power turbine and provide a braking force to the vehicle, wherein at least one of the following is true: (a) the braking device comprises a compressor selectively mechanically engaged and disengaged from the free power turbine and/or the transmission of the vehicle by a clutch assembly: (b) the braking device comprises a continuously variable transmission; (c) the braking device comprises an electrical generator configured to generate a selected amount of electrical energy; (d) the braking device comprises at least one of an eddy current clutch and an eddy current brake; and (e) the braking device comprises a fluid pump circuit.
 2. The system of claim 1, wherein the transmission comprises: a first gear assembly comprising a high speed bull gear in mechanical communication with a first shaft, a high speed pinion gear in mechanical communication with the free power turbine, and a power take off pinion gear in mechanical communication with the braking device, the high speed bull gear being in mechanical communication with the high speed pinion and the power takeoff pinion; and a second gear assembly comprising a low speed bull gear in mechanical communication with a second shaft and a low speed pinion in mechanical communication with the first shaft, the low speed bull gear being in mechanical communication with the low speed pinion.
 3. The system of claim 2, wherein the transmission comprises: a clutch assembly to selectively engage and disengage the braking device with the transmission wherein: in a normal driving mode, the clutch assembly disengages the braking device from the transmission; and in a braking mode, the clutch assembly engages the braking device with the transmission.
 4. The system of claim 2, wherein (a) is true.
 5. The system of claim 4, wherein the braking compressor comprises at least one of an inlet and outlet nozzle of a variable area, and wherein: in a normal driving mode, the nozzle has a first cross-sectional area normal to gas flow; and in a braking mode, the nozzle has a second cross-sectional area normal to gas flow, the first cross-sectional area being different from the second cross-sectional area, wherein less power is dissipated by the braking compressor in the normal driving mode than in the braking mode.
 6. The system of claim 5, wherein output gas from the braking compressor is at least one of used to charge a pneumatic storage tank and quench a hot gas from a recuperator to assist in engine turndown, the output gas being introduced into an exhaust flow upstream of an input to a hot side of the recuperator.
 7. The system of claim 1, wherein (b) is true and wherein the continuously variable transmission is positioned mechanically between a load and the free power turbine.
 8. The system of claim 7, further comprising an increasing gearbox positioned mechanically between the continuously variable transmission and a braking compressor.
 9. The system of claim 7, further comprising a clutch assembly to selectively engage and disengage the continuously variable transmission from mechanical communication with the free power turbine and the transmission.
 10. The system of claim 1, wherein (c) is true, wherein the electrical generator is configured to generate the electrical energy in response to free power turbine rotation.
 11. The system of claim 10, wherein a control excitation of the electrical generator is controlled to generate the selected amount of electrical energy and wherein the generated electrical energy is carried via a conductive path to at least one of a dynamic braking grid, an electrical energy storage system, and a thermal energy storage device.
 12. The system of claim 11, wherein the generator is positioned mechanically between a clutch assembly and a braking compressor.
 13. The system of claim 1, wherein (d) is true.
 14. The system of claim 13, wherein the braking device comprises an eddy current clutch positioned mechanically between a load and the free power turbine and wherein the eddy current clutch comprises: an exciter armature rigidly connected to an input shaft and at least one diode; a main field coil mechanically connected to the at least one diode; a main armature rigidly connected to an output shaft; and an exciter field coil, the exciter field coil being substantially fixed relative to the free power turbine and activated by one of a direct current and alternating current control system; wherein the exciter armature is electrically connected to the at least one diode by one of an alternative current and direct current wire and the at least one diode is electrically connected to the main field coil by the other of an alternating current and direct current wire; and wherein the exciter armature, at least one diode and main field coil rotate when the input shaft rotates.
 15. The system of claim 1, wherein (e) is true.
 16. The system of claim 15, wherein the fluid pump circuit is engaged mechanically with the free power turbine and comprises: a fluid pump; and a restrictor valve having a variable orifice size, wherein the orifice size is varied to provide a variable retarding force on at least one of the free power turbine and the transmission.
 17. The system of claim 16, wherein the pump is in mechanical and fluid communication with a lubrication system of at least one of the engine and the transmission.
 18. The system of claim 1, further comprising: a spur gear mechanically connected to the braking device; a plurality of planet gears; a planet carrier in mechanical communication with the plurality of planet gears; a sun gear in mechanical communication with plurality of planet gears; and a ring gear in mechanical communication with the spur gear and the plurality of planet gears, wherein the spur gear is in mechanical communication with a first braking device, wherein the sun gear is in mechanical communication with a second braking device, and wherein a low input shaft is in mechanical communication with the planet carrier and a clutch assembly to selectively engage and disengage the first and second braking devices from mechanical communication with the free power turbine and the transmission.
 19. In a vehicle comprising a gas turbine engine and a transmission comprising at least one turbo-compressor spool assembly, the at least one turbo-compressor spool assembly comprising a compressor in mechanical communication with a turbine, the turbine outputting a gas, a free power turbine in fluid communication with the turbine, the free power turbine being driven by the outputted gas, and a braking device in mechanical communication with the free power turbine and the transmission, a method comprising: performing at least one of the following steps: (a) in response to a sensed revolutions-per-minute of the free power turbine, selectively engaging and disengaging a braking device from mechanical communication with the free power turbine, the braking device retarding rotation of the free power turbine; (b) in response to a sensed braking request of the vehicle, selectively engaging and disengaging a braking device from mechanical communication with the free power turbine, the braking device providing a braking force to the vehicle; (c) varying, by an continuously variable transmission, a gear ratio continuously between first and second gear ratios, the gear ratio being for a mechanical linkage between a braking device and the clutch assembly; (d) generating, by an electrical generator, a selected amount of electrical energy to provide at least one of a selected amount of retardation force against rotation of the free power turbine and a selected amount braking force to the vehicle; (e) applying torque by at least one of an eddy current brake and eddy current clutch to provide at least one of a selected amount of retardation force against rotation of the free power turbine and a selected amount braking force to the vehicle; and (f) intermittently operating a fluid pump in mechanical communication with the free power turbine to provide at least one of a selected amount of retardation force against rotation of the free power turbine and a selected amount braking force to the vehicle.
 20. The method of claim 19, wherein the braking device is selectively mechanically engaged and disengaged from the free power turbine and/or the transmission of the vehicle by a clutch assembly and wherein the transmission comprises: a first gear assembly comprising a high speed bull gear in mechanical communication with a first shaft, a high speed pinion gear in mechanical communication with the free power turbine, and a power take off pinion gear in mechanical communication with the braking device, the high speed bull gear being in mechanical communication with the high speed pinion and the power takeoff pinion; and a second gear assembly comprising a low speed bull gear in mechanical communication with a second shaft and a low speed pinion in mechanical communication with the first shaft, the low speed bull gear being in mechanical communication with the low speed pinion.
 21. The method of claim 20, further comprising: selectively disengaging the braking device with the transmission in a normal driving mode; and selectively engaging the braking device with the transmission in a braking mode.
 22. The method of claim 19, wherein at least one of step (a) and step (b) is performed.
 23. The method of claim 22, wherein the braking device comprises at least one of an inlet and outlet nozzle of a variable area and wherein: in a normal driving mode, the nozzle has a first cross-sectional area normal to the at least a portion of the gas flow; and in a braking mode, the nozzle has a second cross-sectional area normal to gas flow, the first cross-sectional area being different from the second cross-sectional area, wherein less power is dissipated by the braking device in the normal driving mode than in the braking mode.
 24. The method of claim 23, wherein output gas from the braking compressor is at least one of used to charge a pneumatic storage tank and quench a hot gas from a recuperator to assist in engine turndown, the output gas being introduced into an exhaust flow upstream of an input to a hot side of the recuperator.
 25. The method of claim 19, wherein step (c) is performed.
 26. The method of claim 25, further comprising positioning an increasing gearbox positioned between the continuously variable transmission and a braking compressor.
 27. The method of claim 26, wherein step (d) is performed.
 28. The method of claim 19, wherein a control excitation of the electrical generator is controlled to generate the selected amount of electrical energy and wherein the generated electrical energy is carried via a conductive path to at least one of a dynamic braking grid, an electrical energy storage system, and a thermal energy storage device.
 29. The method of claim 27, wherein the generator is positioned mechanically between a clutch assembly and a load.
 30. The method of claim 19, wherein step (e) is performed.
 31. The method of claim 20, wherein the at least one of eddy current brake and clutch is the eddy current clutch and wherein the eddy current clutch comprises: applying one of a direct and alternating electrical current to an exciter field coil to induce the other of a direct and alternating current in an exciter armature; rectifying the induced current to the one of direct and alternating current and causing the one of the direct and alternating current in a main field coil; causing a rotational force in a main armature; wherein the exciter armature and main field coil rotate when an input shaft rotates and the main armature rotates when an output shaft rotates.
 32. The method of claim 19, wherein step (f) is performed.
 33. The method of claim 32, wherein the fluid pump is in communication with a restrictor valve having a variable orifice size, wherein the orifice size is varied to provide a variable retarding force on at least one of the free power turbine and the transmission.
 34. The method of claim 33, wherein the fluid pump is in mechanical communication with a lubrication system of at least one of the engine and the transmission.
 35. The method of claim 20, wherein the braking device further comprises: a spur gear mechanically connected to the braking device; a plurality of planet gears; a planet carrier in mechanical communication with the plurality of planet gears; a sun gear in mechanical communication with plurality of planet gears; and a ring gear in mechanical communication with the spur gear and the plurality of planet gears, wherein the spur gear is in mechanical communication with a first braking device, wherein the sun gear is in mechanical communication with a second braking device, and wherein a low input shaft is in mechanical communication with the planet carrier and clutch assembly to selectively engage and disengage the first and second braking devices from mechanical communication with the free power turbine and the transmission.
 36. A vehicle, comprising: (a) an engine; (b) a transmission; (c) a braking device to maintain or reduce the ground velocity of the vehicle; and at least one of the following braking device control devices: (C1) a continuously variable transmission positioned mechanically with respect to the braking device, the transmission and the engine; (C2) an electrical generator configured to generate a selected amount of electrical energy to provide a selected amount of retardation force against rotation of a shaft of the engine; (C3) at least one of an eddy current clutch and eddy current brake positioned mechanically with respect to the braking device, the transmission and the engine; and (C4) a pump and restrictor valve in fluid communication with the braking device.
 37. The vehicle of claim 36, wherein the engine is a gas turbine engine and comprises at least one turbo-compressor spool assembly, wherein the at least one turbo-compressor spool assembly comprises a compressor in mechanical communication with a turbine, the turbine outputting a gas and a free power turbine in fluid communication with the turbine, the free power turbine being driven by the outputted gas, wherein the braking compressor is in mechanical communication with the free power turbine to dissipate power of the free power turbine.
 38. The vehicle of claim 37, wherein the transmission comprises: (B1) a first gear assembly comprising a high speed bull gear in mechanical communication with a first shaft, a high speed pinion gear in mechanical communication with the free power turbine, and a power take off pinion gear in mechanical communication with the braking compressor, the high speed bull gear being in mechanical communication with the high speed pinion and the power takeoff pinion; and (B2) a second gear assembly comprising a low speed bull gear in mechanical communication with a second shaft and a low speed pinion in mechanical communication with the first shaft, the low speed bull gear being in mechanical communication with the low speed pinion.
 39. The vehicle of claim 36, further comprising: (C3) a clutch assembly to selectively engage and disengage the braking compressor with the transmission wherein: in a normal driving mode, the clutch assembly disengages the braking compressor from the transmission; and in a braking mode, the clutch assembly engages the braking compressor with the transmission.
 40. The vehicle of claim 37, wherein the braking compressor comprises at least one of an inlet and outlet nozzle of a variable area, and wherein: in a normal driving mode, the nozzle has a first cross-sectional area normal to gas flow; and in a braking mode, the nozzle has a second cross-sectional area normal to gas flow, the first cross-sectional area being different from the second cross-sectional area, wherein less power is dissipated by the braking compressor in the normal driving mode than in the braking mode.
 41. The vehicle of claim 40 wherein output gas from the braking compressor is at least one of used to charge a pneumatic storage tank and quench a hot gas from a recuperator to assist in engine turndown, the output gas being introduced into an exhaust flow upstream of an input to a hot side of the recuperator.
 42. The vehicle of claim 37, wherein (C1) is true.
 43. The vehicle of claim 42, further comprising an increasing gearbox positioned mechanically between the continuously variable transmission and a braking compressor.
 44. The vehicle of claim 42, further comprising a clutch assembly to selectively engage and disengage the continuously variable transmission from mechanical communication with the free power turbine and the transmission.
 45. The vehicle of claim 37, wherein (C2) is true.
 46. The vehicle of claim 45, wherein a control excitation of the electrical generator is controlled to generate the selected amount of electrical energy and wherein the generated electrical energy is carried via a conductive path to at least one of a dynamic braking grid, an electrical energy storage system, and a thermal energy storage device.
 47. The vehicle of claim 46, wherein the generator is positioned mechanically between a clutch assembly and a braking compressor.
 48. The vehicle of claim 37, wherein (C3) is true.
 49. The vehicle of claim 48, wherein the eddy current clutch comprises: an exciter armature rigidly connected to an input shaft and at least one diode; a main field coil mechanically connected to the at least one diode; a main armature rigidly connected to an output shaft; and an exciter field coil, the exciter field coil being substantially fixed relative to the free power turbine and activated by one of a direct current and alternating current control system; wherein the exciter armature is electrically connected to the at least one diode by one of an alternative current and direct current wire and the at least one diode is electrically connected to the main field coil by the other of an alternating current and direct current wire; and wherein the exciter armature, at least one diode and main field coil rotate when the input shaft rotates.
 50. The vehicle of claim 37, wherein (C4) is true.
 51. The vehicle of claim 50, wherein the fluid pump circuit comprises: a fluid pump; and a restrictor valve having a variable orifice size, wherein the orifice size is varied to provide a variable load on the free power turbine.
 52. The vehicle of claim 51, wherein the pump is in mechanical communication with a lubrication system of at least one of the engine and the transmission.
 53. The braking device of claim 37, wherein the transmission comprises: (B1) a spur gear mechanically connected to the braking compressor; (B2) a plurality of planet gears; (B3) a planet carrier in mechanical communication with the plurality of planet gears; (B4) a sun gear in mechanical communication with plurality of planet gears; and (B5) a ring gear in mechanical communication with the spur gear and the plurality of planet gears, wherein the spur gear is in mechanical communication with a first braking device, wherein the sun gear is in mechanical communication with a second braking device, and wherein a low input shaft is in mechanical communication with the planet carrier and a clutch assembly to selectively engage and disengage the first and second braking devices from mechanical communication with the free power turbine and the transmission.
 54. A tangible or non-transient computer readable medium comprising microprocessor-executable instructions operable to perform at least the following steps: a) sensing at least one of a revolutions per minute (“rpms”) of a free power turbine, at least one of an on and off state of a braking device clutch, at least one of an on and off state of a transmission clutch, and a braking device control setting; b) based on the sensed at least one of a revolutions per minute (“rpms”) of a free power turbine, at least one of an on and off state of a braking device clutch, at least one of an on and off state of a transmission clutch, and a braking device control setting, determining that the free power turbine requires over-speed control; c) in response to step (b), disengaging the transmission clutch and engaging the braking device clutch; d) reducing the rpms of the free power turbine by controlling an amount of energy dissipation of the braking device; e) during step (d), sensing rpms of the free power turbine and reducing the rpms of the free power turbine until the rpms of the free power turbine are reduced to less than or equal to a selected value; and f) when the rpms of the free power turbine are less than the selected value, disengaging the braking device clutch.
 55. A tangible or non-transient computer readable medium comprising microprocessor-executable instructions operable to perform at least the following steps: a) sensing at least one of an on and off state of braking device clutch, at least one of an on and off state of a transmission clutch, a vehicle ground velocity, a transmission gear setting, and a braking device control setting; b) based on the sensed at least one of a vehicle ground velocity, at least one of an on and off state of a braking device clutch, at least one of an on and off state of a transmission clutch, and a braking device control setting, determining that engine braking is required; c) in response to step (b), engaging the braking device clutch and engaging the transmission clutch for engine braking; d) increasing a vehicle braking force opposing a direction of motion of the vehicle by controlling an amount of energy dissipation of the braking device; e) during step (d), sensing a vehicle ground velocity and applying the engine braking force until the vehicle ground velocity is less than or equal to a selected value; and f) when the vehicle ground velocity is less than or equal to the selected value, disengaging the braking device clutch. 